Preparation of chemical cellulose for esterification



Jan. 29,1946. D. J. KRIDEL 2,393,783

PREPARATION OF CHEMICAL CELLULQSE FOR ESTERIFICATION Filed Aug. 24, 1945FIG. I.

FIG.2.

DONALD J. KRIDEL INVENTOR Y M f MC) I Patented Jan. 29, 1946 PREPARATIONOF CHEMICAL CELLULOSE FOR ESTERH ICATION Donald J. Kridel, Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, N. Y., a corporationof New Jersey Application August 24, 1943, Serial No. 499,870

2 Claims.

This invention relates to the fiufling and drying of cellulose prior toits nitration by subjecting the cellulose in wet form to a violent blastof compressed gas, such as compressed air, followed by subjecting to acurrent of drying gases to re-. move the moisture therefrom.

Ordinarily in the manufacture of chemical cellulose, for instance, inthe making of wood pulp, the material is dried while in a compact webform. The material is ordinarily produced in sheet or board form, thefibers being in contact with one another while in a highly plasticcondition during the drying operation, consequently the cellulosefibersare firmly bonded together in the final product. In the preparation ofrefined cotton linters, the linters are obtained in a wet condition andare squeezed to the lowest possible water content and then dried. Byeither method lumps or aggregates are obtained which usuallynecessitates extensive picking or shredding operations to assuresatisfactory yield and uniformity upon esterification.

Various methods of disintegrating the dried cellulose have beenproposed. Although cellulose has been fluffed by these methods,ordinarily they result in considerable fracture of the individual fiber.A non-uniform product is usually obtained and dustiness isencountered.Numerous tearing and shredding patents evidence the interest in I thedisintegration of dried cellulose which has been manifested in recentyears.

Ordinarily cellulose nitration processes are made up of a combination ofan esterification and a hydrolysis operation carried out simultaneously.Both of these operations are very dependent as to velocity and degree ofcompletion upon the water content of the nitrating acid in the reactionzone. A change of as little as 0.1% in water content will noticeablychange the nitrogen content of the ester and will also'cause greaterhydrolysis as evidenced by lower viscosity and yield of production.

Water is a by-product of the esterification reaction. If the waterformed thereby is localized rather than diffusing from the reaction zonesurrounding the cellulose aggregate or fiber into the main body oftheacid, the increase in water content will'cau'se excessive hydrolysis.This excessive hydrolysis may be avoided by one of two methods:

1. By increasing the nitric acid content of the nitrating acid, thishydrolysis effect may be aileviated. This is probably due to thecellulose nitrate being less susceptible to hydrolysis than is theunesterified cellulose. Apparently the increased nitric acid content ofthe acid speeds up the rate of esterification and the overall hydrolysiseffect is diminished. This method is employed in nitrating chipped orcut wood cellulose sheets. The nitric acid employed in such nitratingbaths is often as high as 28% as compared to 16-22% ordinarily used inthe nitration of cotton linters. The retained acid costs in thesenitrations are consequently higher due to the relatively high value ofnitric acid. 2. By separating the cellulose fibers from each other so asto eliminate mats and clusters, the cellulose isput into condition tofacilitate the diffusion of the water of reaction out of the reactionzone into the main body of the acid. The ultimate point is that at whichthe cellulose exists entirely as separate fibers.

One object of my invention is to provide a method of forming a flulfeddry chemical cellulose which fits in well with present day pulpmanufacture. Another object of my invention is to provide a method offorming a fluffed dry chemical cellulose which provides for drying ofthe pulp in separated condition avoiding matting or adherence of thefibers. A still further object of my invention is to provide cellulosein a form in which it can be nitrated uniformly and with nitrating acidsof low nitric acid content. Other objects of my invention will appearherein.

I have found that if cellulose in a matted or aggregate form is made wetand then subjected to a violent blast of gas, such as a blast ofcompressed air, that the cellulose is blown up into separate fiberswhich fibers pass through the highly plastic wet stage as individualfibers and cementing of the fibers does not occur during the dryingoperation. The wet fibers are in a form in which they can be carriedalong by a current of air such as in a drying operation and theresulting product is eminently suitable for use immediately in anitrating process or it may be baled or compressed while still retainingits characteristics as a batch or mass of individual fibers and may beemployed as desired.

As most pulp mills are set up to turn out the pulp in the form of asheet or board, my process fits in wellwith present day practice in pulpmanufacture. My fiufiing process may be carried out directly upon thepulp board in the mill so that drying is unnecessary or it may be usedupon the dry pulp sheet as supplied by the manufacturer, in the lattercase wetting of the pulp sheet being necessary. Also if cotton lintersare treated by my process either the linters may-be fiuffed in their wetconditions in the mill in which the linters are refined for use inesterification processes or the dried linters may be thoroughly wettedand run through a drying process'in accordance with my invention.

The drawing illustrates apparatus which is very suitable for carryingout my invention. Fig. 1 is a flow sheet of a combination of apparatusin which the cellulose is fluffed' and carried by drying gases into abin or storage compartment. Fig. 2 is a representation in section of theportion of the apparatus where the wetcellulose is subjected to a blastof air, or other inert gas to blow. it up or cause the fibers toseparate from each other. The drawing illustrates the preferred mannerof subjecting the wet cellulose to a blast of gas which involvessubjecting the cellulose to the action of two impinging jets of airunder high pressure. In the apparatus the cellulose such as in the formof a wet pulp sheet I2 is borne along by an endless conveyer l motivated by roll II. A pressure roll I la is also pro vided to assist infeeding the sheet into the apparatus. Pipes"l5 supply jets H with "comepressed airor other ompressed gas at hig pressure, the jets [beingranged so that the impinge with the wet cellulosic sheet introduced atthe line of intersection. In the apparatus shown the fiufling occursin'chamber l3 and the air stream introduces the fibers from this chamberinto a current of, conveying and drying air at point 26 which, as shownin the apparatuspis 'a Venturi constriction in the duct. A circulatinfan I1 is present in the line and the fibers are introduced at thesuction side of this fan. "'The fibers are circulated through conduitsl6 and I 8 and are deposited in the bin l9. Bin I S'is pro-' vided witha screen arrangement-.20 to allow the air to escape from the fibers,some of the air escaping through the vent He and some being introducedinto passage 22. The bin is also provided with an outlet at the bottomso that the fibers may be withdrawn by means of discharge valve' 2|. Theair which is withdrawn from the bin by conduit 22 passes through apreheater'23 in which the air is heated by means of a steam coil 24. Theair then passes through conduit 25 to Venturipoint 26 where it takes afresh supply 0f fiuifed cellulose. The apparatus may be operatedcontinuously, the rate at which it is running depending upon variousfactors such as the rate at which the cellulose is fed into theapparatus, the pressure of the impinging blasts and the rate ofcirculation of the drying gases through the apparatus. It is desirablethat the air at |9a be vented as rapidly as the compressed air is takenin through the jetsv H. In this way the moisture evaporated from thefibers is being continuously moved from the apparatus and the air,therefore, retains its drying properties. If desired, a drying unit maybe inserted in con: duit 22 so that the air heated in preheater 23 haslittle or no moisture therein. This, however, is not ordinarilynecessary unless high speed operation of the apparatus is desirable.

It is desirable that the cellulose which is intrqduced be sufllcientlywet so that it is in a soggy condition in order to give the bestresults. 0b-

' viously, however, this is a matter for the judgment of the individualoperator and in some cases it may be that a lower moisture content wouldbe desirable than in other cases.

'I'hefollowing example illustrates the preparing of cellulose nitrateemploying my invention", A sheet of refined wood pulp cellulose of goodwhiteness and having an a-cellulose content of 90% was moistened so asto have a water content of 60%. This material was then subjected to the.action of a blast of air of approximately 50 lbs.. pressure. Theflufied' material is then blown into. a collector by drying air. Whenthe material had dried satisfactorily, it was subjected to nitration byintroducing it into a nitrating acid containing 20% nitric acid, 2.5%NzO4.and 60% H2804. A cellulose nitrate was prepared having a nitrogencontent of 12.01% and a viscosity of 33 seconds. The yield was 94% oftheoretical. The resulting product, after stabilization, was found todissolve up giving a brilliant solution completely freeof undissolvedfibers and ch'its.

Yarious advantages reside in the use of the product prepared inaccordance with my invention for preparing cellulose nitrate. These in-4 clude 1. Lower nitric acid content nitrating agents may be usedeffecting a lower cost of retained acid costs and a saving in total acidusage. For in stance, for nitrating the fiuifed cellulose in accordancewith my invention, nitrating acids may be employed having a nitric acidcontent of 16- 22%. Any of the nitrating acids specified in TalbotPatent No. 2,118,275 may be employed for nitrating the cellulosematerial obtained as described.

2. A more uniform nitration is accomplishedprobably resulting in greaterproduct strength. This appears to be due, amongother things, to

the uniform distribution of the nitrating acid viscosity lowering at agiven subjecting the wood throughout the cellulose.

3. Higher yields of nitrate are obtained than upon other cellulosestarting materials with a nitrating acid having the same nitric acidcontent.

4. The resulting cellulose nitrate exhibits less temperature than isfound to. be true with other cellulose starting materials. Thischaracteristic is an advantage in a process in which a high viscositycellulose nitrate is desired such as in cellulose nitrate for munitions.Although the drying process described and illustrated herein fits invery well with the fiufl'ed cellulose as it is easily carried alongby acurrent of'drying gas, other drying processe may be employed,particularly where the cellulose i permitted to remain in flufiedcondition. Alth'o'ugh my invention is particularly concerned withpreparing cellulose for nitration processes, the resulting product isalso opened up so that it may be employed in processes in which organicacid esters of cellulose are prepared.

Iclaim:

1. A method of converting wood pulp board to a form suitable foresterification which comprises pulp board while containing at least 60%water directly to a violent blast of compressed air so as to causeblowing apart of the fibers of the cellulose pulp and whilein theresulting highly plastic, blown-apart condition,

conveying the pulp by means of drying air so as to remove the moisturetherefrom and ther by assure the absence of compact lumps therel 2. Amethod of converting chemical cellulose board to a form suitable foresterlfication which comprises subjecting the cellulose board whilecontaining at least 60% water directly to a violent blast of inert gasso as to cause blowing apart of the fibers of the" cellulose board andwhile in the resulting highly plastic, blown-apart condition, drying thefibers by means of drying gases so as to remove the moisture therefromand thereby assure the absence f compact lumps therein;

DONALD J. KRIDEL.

